Many organic acids and amino acids, including glutamic acid and glycolic acid, are useful for stimulating plant growth. For example, in 1980, Tillberg (Physiol. Plant 50:158-160) reported that duckweed growth was stimulated by 10 to 20% when low levels of glycolic acid (30-220 ppm) were added to culture media, although levels of 380 ppm or higher were inhibitory to growth.
Oligomers of glycolic acid which are hydrolyzed to monomers have also been reported to stimulate duckweed growth (Kinnersley et al., U.S. Pat. No. 4,813,997). Behrend & Meteles (1975, Plant Physiol. 56:584-589) found that glutamic acid increased the growth of cell cultures of tobacco, tomato, and carrot, however, the effects of this amino acid on intact plants are less clear. Gorham (1950, Canadian J. of Research 28:356-381) found that glutamic acid (100 ppm) had negative effects on plant growth.
While increasing vegetative plant growth is important, of much greater significance is stimulation of reproductive growth that gives increased yield of fruits, vegetables, grains, etc. Compositions of organic acids that increase plant productivity, and in particular that increase reproductive growth, are therefore needed. The present invention addresses this need.